1. Field
This disclosure generally relates to repeaters in wireless communication systems.
2. Background
Wireless communication systems and techniques have become an important part of the way we communicate. However, providing coverage can be a significant challenge to wireless service providers. One way to extend coverage is to deploy repeaters. In general, a repeater is a device that receives a signal, amplifies the signal, and transmits the amplified signal. A typical repeater configuration includes a donor antenna as an example network interface to network infrastructure such as a base station. The repeater also includes a server antenna (also referred to as a “coverage antenna”) as a mobile interface to one or more mobile devices. In operation, the donor antenna is in communication with the base station, while the server antenna is in communication with one or more mobile devices. Signals from the base station are amplified using forward link circuitry, while signals from the mobile devices are amplified using reverse link circuitry. Many configurations may be used for the forward link circuitry and the reverse link circuitry.
There are many types of repeaters. In some repeaters, both the network and mobile interfaces are wireless; while in others, a wired network interface is used. Some repeaters receive signals with a first carrier frequency and transmit amplified signals with a second different carrier frequency, while others receive and transmit signals using the same carrier frequency. For “same frequency” repeaters, one particular challenge is managing the feedback that occurs since some of the transmitted signal can leak back to the receive circuitry and be amplified and transmitted again. Existing repeaters manage feedback using a number of techniques, including physical isolation between the donor and server antennae and echo cancellation techniques.
Wireless service providers continue to face issues such as inadequate indoor 3G voice and data coverage, especially in homes and SOHOs (Small Offices, Home Offices). Repeaters have a long history in wireless networks, with mixed results. Very large infrastructure related repeaters have been successfully deployed to fill coverage holes and reduce total base station sites during initial deployments. However, personal repeaters (indoor self installation type) have not been successfully adopted broadly in the market due to a number of factors. One issue which impacts the deployments of personal repeaters in congested areas is “pilot pollution”, or other interfering signals. Pilot pollution is the situation when too many base stations are received at the mobile or the repeater's receiver causing a reduction in signal quality. While many 3G systems use soft hand off, there are limits to when the soft hand off approach provides benefit, and when too many signals are simply interference. Further, for data optimized systems, such as 1XEV-DO, and 4G systems, such as LTE, soft handoff is often not used, opting rather for a fast selection diversity between base stations.
The interfering condition of too many signals at a receiver is especially problematic for “same frequency” repeaters because boosting the signal may simply amplify and broadcast a poor signal-to-noise ratio (SNR) signal which may not be beneficial in some cases. Generally a repeater cannot improve the quality of the signal it receives and in the condition of strong signal level, but significant interference, a repeater may not provide significant benefit because the repeater would only cause an increase in the interfering noise of the system.